Movement classifications

Drawing inspiration from Lenoir & Svenning, we aim to characterize general distribution change patterns in species from the NEFSC Bottom Trawl Survey.

Directional movement

Characterizing distributions

Distribution changes are characterized by the movement trends of the 5th, 50th, and 95th percentiles (representing distibution edges).

• Stable: All edges and centroid are stable.

• March: All edges and centroid are showing movement in the same direction (northward, southward)

• Expand: The centroid is stable and edges are moving away from each other.

• Contract: The centroid is stable and edges are moving towards each other.

• Lean: The centroid and one edge are moving in the same direction.

• Retract: The centroid and one edge are stable while one edge moves towards the centroid.

Rate of movement

Now we want to explore the magnitude of species movement, coupled with their directional trends, to ultimately compare distribution changes of predator and prey species. We could compare rates of centroid movement, or edges-only.